Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$222.58	4.179%	$231.8816	$231.88	$231.90	$231.90
Purchase #2	$54.64	3.612%	$56.6136	$56.61	$56.60	$56.60
Purchase #3	$90.25	11.661%	$100.7741	$100.77	$100.75	$100.80
Purchase #4	$12.78	11.508%	$14.2507	$14.25	$14.25	$14.30
Purchase #5	$230.54	9.806%	$253.1468	$253.15	$253.15	$253.10
Purchase #6	$215.36	3.289%	$222.4432	$222.44	$222.45	$222.40
Purchase #7	$115.89	12.103%	$129.9162	$129.92	$129.90	$129.90
7 purchase totals =	$942.04		$1,009.0262	$1,009.02	$1,009.00	$1,009.00